hfs - reducing fruit drop in fruit trees with tpa (drinnan)era.daf.qld.gov.au/id/eprint/5498/1/hfs -...
TRANSCRIPT
Reducing fruit drop in fruit trees with the syntheticauxin TPA
Agri-Science Queensland Innovation Opportunity
July 2016
This publication has been compiled by James Drinnan of Horticulture and Forest Science, Department of Agriculture andFisheries.
© State of Queensland, 2015
The Queensland Government supports and encourages the dissemination and exchange of its information. The copyright inthis publication is licensed under a Creative Commons Attribution 3.0 Australia (CC BY) licence.
Under this licence you are free, without having to seek our permission, to use this publication in accordance with the licenceterms.
You must keep intact the copyright notice and attribute the State of Queensland as the source of the publication.
Note: Some content in this publication may have different licence terms as indicated.
For more information on this licence, visit http://creativecommons.org/licenses/by/3.0/au/deed.en
The information contained herein is subject to change without notice. The Queensland Government shall not be liable fortechnical or other errors or omissions contained herein. The reader/user accepts all risks and responsibility for losses,damages, costs and other consequences resulting directly or indirectly from using this information.
Summary
The project investigated if the synthetic auxin 3, 5, 6 - trichloro-2-pyridyloxyacetic acid (TPA) could be
used to reduce fruit drop in mango, avocado or macadamia. Recent research has found that TPA can
significantly reduce fruit drop and increase yields in a range of lychee varieties by inhibiting the
development of the fruit abscission layer. Fruit drop is a problem in mango, avocado and macadamia
reducing maximum potential yields. Application rates and timings for the trial work were adapted from
the lychee research trials. Fruit at various stages of development were treated with a single foliar
spray of TPA at 50 ppm and the level of fruit drop recorded. In avocado there was very little natural
fruit drop in either the Hass or Sheppard variety in this season therefore the effect of TPA on fruit drop
could not be determined, there were indications that the rate of TPA was too high with some
phytotoxicity on the leaves. In mango fruit drop was greatly reduced with TPA applications however
many of the fruit failed to develop properly, either dying or abscising before harvest in the young fruit
or remaining until harvest but poorly formed and non-commercial in the older fruit. In macadamia fruit
drop was also initially reduced with TPA applications but like mango not all the fruit developed
properly especially in the younger fruit. Young fruit stopped growing and eventually abscised before
harvest, in the older fruit, development was less effected and fruit was held until harvest, however
most of this fruit was not of sufficient quality to warrant harvest. Some phytotoxic effects on young
leaves were also observed. Lower rates and later application times of TPA to overcome some of the
fruit development issues encountered in this research are suggested in future work.
Document title, Department of Agriculture and Fisheries, 2016 1
Table of contents
Background ............................................................................................................................................ 2
Project Objectives.................................................................................................................................. 2
Methodology........................................................................................................................................... 2
Results .................................................................................................................................................... 4
Conclusions/Significance/Recommendations.................................................................................... 9
Key Messages ......................................................................................................................................10
Where to next .......................................................................................................................................10
Budget Summary .................................................................................................................................10
Document title, Department of Agriculture and Fisheries, 2016 2
Background
Fruit drop is a significant issue in a number of horticultural crops reducing maximum potential yields.
Most crops will set much more fruit than develop to full maturity and some drop is inevitable and
unavoidable. However in many crops in particular varieties and seasons the amount of fruit drop can
be excessive and this can lead to large yield losses. Fruit drop can be due to a number of factors
including poor pollination and fertilisation, poor embryo development or death, climatic factors such as
water stress or unfavourable temperatures during fruit development, excessive plant nitrogen or
competition for resources with other developing fruit or vegetative growth. Whatever the cause, fruit
drop in many cases is manifested by changes in the levels of plant growth regulators either in the fruit
or in the plant. In lychee it has been found that the level of auxin in young fruit falls dramatically just
prior to abscission. The low auxin levels (being an antagonist to abscisic acid) allow abscisic acid
level to increase which facilitates the development of the abscission layer between the plant and the
fruit leading to fruit drop. Recent research has found that by applying the synthetic auxin (TPA)
externally to young fruit of lychee, fruit drop can be significantly reduced and yields increased by up to
50%. TPA has now been registered for use in lychee and is also used in the citrus industry for a
similar purpose. Given the positive responses of TPA in these two crops, research to examine the
effect of TPA on fruit drop in other horticultural crops e.g. avocado, mango or macadamia would seem
warranted.
Project Objectives
Determine if TPA can be used to reduce fruit drop in avocado, mango or macadamia.
Methodology
For each of the crops, fruit at different stages of growth were sprayed with the auxin TPA and the
level of fruit drop recorded. For each crop and each fruit size, forty fruiting panicles or racemes spread
across 5-15 trees were selected and tagged. The number of fruit on each panicle or raceme was
recorded and then half the panicles or racemes were treated with a single foliar spray of TPA at 50
ppm plus wetter, the other half were left as untreated controls. The number of fruit was recorded once
during fruit development and again at harvest. In avocado, fruit 40 mm in length for the variety Hass
and 40-50 mm in length for the variety Sheppard were used (Image 1). In mango, fruit 10-20 mm and
30-40 mm in length in the variety Kensington Pride were used (Image 2) and in macadamia fruit 10
mm and 20 mm in diameter in the variety A16 were used (Image 3). In each of the crops whole trees
were also treated with TPA and observed for the effects on fruit drop and phytotoxicity.
Document title, Department of Agriculture and Fisheries, 2016 3
Image 1 – Stage of fruit development prior to treatment in Hass avocado.
Image 2 – Fruit drop was recorded on tagged racemes.
Document title, Department of Agriculture and Fisheries, 2016 4
Image 3 – Stage of fruit development in mango (10-20 mm) prior to treatment.
Results
Generally TPA reduce fruit drop initially however much of this fruit either subsequently abscised
before harvest or failed to develop into a marketable sized or quality fruit.
In macadamia the high rates of fruit drop were initially reduced by TPA applications from 28.2 to 1.1
% in the 10 mm diameter fruit and from 21.4 to 1 % in the 20 mm diameter fruit (Figure 1). The TPA
treatment however effected normal fruit development particularly in the youngest fruit. In these fruit
the kernels stopped growing and became discoloured, the shell lignified, thickened and hardened
prematurely and the fruit eventually abscised before harvest. A similar observation is seen in lychee
when TPA is applied to fruit younger than the recommended stage of development, indicating that the
time of application may have been too early. In the larger fruit (20 mm) development was also
effected but to a lesser extent and most of the fruit was retained until harvest. Although this led to a
reduced level of fruit drop compared to the control fruit (16 verses 25.4 %), a lot of the kernels were
poorly developed and discoloured and the shell had become very thick and the nuts not commercially
saleable (Image 4).
Document title, Department of Agriculture and Fisheries, 2016 5
Figure 1 – The level of fruit drop between the time of application (10 or 20 mm) and harvest in
macadamia.
0
20
40
60
80
100
10 mm harvest
%Fr
uit
Dro
p
cont
TPA
0
20
40
60
80
100
20 mm harvest
%Fr
uit
Dro
p
cont
TPA
Document title, Department of Agriculture and Fisheries, 2016 6
Image 4 – Fruit from the control and TPA treatment prior to harvest.
Control TPA
In the whole trees treated with TPA, drop sheets indicated a large initial reduction in fruit drop (Image
5), but as the fruit grew, fruit development issues were evident, including reduced growth rates and
fruit size, discoloured small kernels and thick woody shells. In these trees there were also
phytotoxicity symptoms on new vegetative flush with pale strappy leaves typical of damage caused by
auxin based herbicides.
Image 5 – Initial fruit drop on whole trees was greatly reduced with the TPA treatment.
Control TPA
In mango the very high rates of fruit drop were initially reduced by TPA applications, from 40.2 to 20.1
% for fruit 10-20 mm in length and from 42.5 to 25.3 % for fruit 30-40 mm in length (Figure 2). The
development of this fruit however was affected especially the young fruit which all abscised before
harvest. A similar observation is seen in lychee when TPA is applied to fruit younger than the
recommended stage of development, indicating that the time of application may have been too early.
In the older fruit the amount of fruit drop at harvest in the TPA treatments was similar to that in the
controls, however some of this fruit was not marketable because it was small and miss-shaped
(Image 6).
Document title, Department of Agriculture and Fisheries, 2016 7
Figure 2 – The level of fruit drop between the time of application (10-20 or 30-40 mm) and
harvest in mango.
Image 6 – Fruit from the control and TPA treatment prior to harvest.
0
20
40
60
80
100
10-20 mm harvest
%Fr
uit
Dro
p
cont
TPA
0
20
40
60
80
100
30-40 mm harvest
%Fr
uit
Dro
p
cont
TPA
Document title, Department of Agriculture and Fisheries, 2016 8
In the whole trees treated with TPA, drop sheets indicated fruit drop was greatly reduced and there
were no phytotoxic symptoms observed. A lot of fruit retained however was small and poorly formed.
It is most likely that the miss-formed fruit in mango and macadamia was damaged by the TPA
applications but it is also possible that this fruit occurs naturally and the TPA treatment just prevents
this fruit from abscising prior to harvest that would have occurred in the control trees.
In avocado there was very little fruit drop (< 4 %) in fruit sized 40-50 mm in length in either the Hass
or Shepard varieties in the control treatments in this season (Figure 3). This makes it impossible to
determine if TPA had any effect on reducing fruit drop because there was almost none.
In the whole trees treated with TPA there was also very little fruit drop. Some phytotoxic symptoms
were observed on new growth on the Hass variety (Image 7) but none on Shepard.
Figure 3 – The level of fruit drop between the time of application (40-50 mm in Shepard and 40
mm in Hass) and harvest in avocado.
0
20
40
60
80
100
40-50 mm harvest
%Fr
uit
Dro
p
cont
TPA
0
20
40
60
80
100
40 mm harvest
%Fr
uit
Dro
p
cont
TPA
Document title, Department of Agriculture and Fisheries, 2016 9
Image 7 – The TPA treatment caused phytotoxicity in leaves of Hass avocado.
Document title, Department of Agriculture and Fisheries, 2016 10
Conclusions/Significance/Recommendations
The initial reduction in fruit drop in macadamia and mango suggests further work with TPA is
warranted. The phytotoxicity symptoms and damage to young fruit indicates that trials should
investigate lower rates of application e.g. 10-30 ppm and/or later times of application e.g. 20-30 mm
diameter in macadamia and 40-80 mm in length in mango.
The initial timings and rates of applications were adapted from research in lychee being a sub-tropical
fruit tree, however the damage to young fruit and the phytotoxic effects suggest lower rates should be
trialled. Lower rates (10-20 ppm) are used in citrus and in hind sight these rates may have been more
appropriate.
In avocado the low levels of fruit drop in fruit sized 40-50 mm this season made it impossible to
determine if TPA had any effect on reducing fruit drop in the Hass or Shepard variety. Follow up work
in a year with higher rates of fruit drop or on younger fruit where more drop is expected is suggested.
Key Messages
The synthetic auxin TPA has proved a successful tool in reducing fruit drop in lychee and this work
indicates that it may have a role to play in reducing fruit drop in other fruit trees. Although the results
of these trials did not lead to higher yields in any treatment, there was enough evidence in mango and
macadamia that TPA does influence fruit drop and that further work with lower rates and different
times of application is warranted.
Where to next
A project concept proposal for further work on TPA in macadamia has been developed for submission
to Horticulture Innovation Australia. Further work in mango and avocado is also proposed.
Budget Summary
$12 000 was originally budgeted for this project. The bulk of this money was for the contribution
toward the use of a vehicle, computer, phone and administration costs. Other budgeted items
included consumables, chemicals, spraying equipment and compensation to growers for lost yield.
Vehicle and computer contribution costs were not charged to the project. The macadamia and
avocado growers did not want compensation for yield loss and mango trees on South Edge Research
Station were used at no cost. Chemicals were donated by Colin Campbell Chemicals.
Approximately $650 was spent on spray equipment and consumables.